Analog Signaling (E & M, DID, FXS, FXO)

Introduction

Hierarchical Navigation

An FXS interface supplies ring, voltage, and dial tone for basic telephone equipment, keysets, and PBXs. An FXO interface is used for trunk, or tie line, connections to a PSTN CO or to a PBX that does not support E&M signaling (when local telecommunications authority permits). This interface is of value for off-premise station applications.

FXO and FXS interfaces indicate on-hook or off-hook status and the seizure of telephone lines by one of two access signaling methods: loop start or ground start. The type of signaling is determined by the type of service from the CO; standard home telephone lines use loop start, but business telephones can order ground start lines instead.